Bone loss is a major, frequent and often permanent comorbid medical complication of anorexia nervosa (AN) affecting over half of all women with this disease and resulting in debilitating fractures, yet there are few effective therapies. In this proposal, we will test the effectiveness of a sequential therapeutic regimen designed to specifically: 1) reverse insulin-like growth factor 1 deficiency, thereby stimulating bone formation, and 2) reduce bone breakdown, using a bisphosphonate, a medication that is effective at reversing bone loss. PUBLIC HEALTH RELEVANCE: Anorexia nervosa affects from 0.5-1.0% of college-age women and is complicated by severe bone loss, with a reduction of bone mineral density (BMD) by at least 1.0 SD in over 90% and by at least 2.5 SD in over one- third of patients. Moreover, anorexia nervosa is associated with a 30% prevalence of fractures. Effective therapies for this complication are needed. This proposal addresses this important public health problem with a randomized, placebo-controlled study of promising therapies for bone loss in this population, which is resistant to traditional approaches.